The control of materials in microscale quantities is of interest in a wide range of fields. Chemical and biological processes such as enzymatic assays, protein identification, and combinatorial synthesis, for example, present the problem of having microscale quantities of material that have to be controlled. The control can include capture of small quantities of an analyte, and localized, precise heating, for example. In other cases, materials have to be moved. Manipulation, including movement, of microscale quantities of materials including liquids, is also of interest in MEMs applications.
Microfluidics is a particular area of microscale material control that has drawn much attention. Typical microfluidic devices include patterned fluidic circuits having microchannels that transport microscale quantities of liquids. Such systems are contemplated for use in so-called “lab on a chip” applications.
The manipulation of discrete droplets is an alternative approach. Through independent micro-manipulation of discrete droplets, complex procedures can be carried out in a manner that directly mimics traditional bench-top protocols. Actuation of individual droplets on solid surfaces has been accomplished by a number of techniques including the use of thermocapillary effects, photochemical effects, electrochemical gradients, surface tension gradients, temperature gradients, air pressure, structured surfaces, dielectrophoresis, and electrostatic methods.
Some techniques have been reported for manipulating freely suspended microliter or nanoliter droplets. One technique involves the electrowetting-based transport of aqueous electrolyte droplets in a silicone oil media using a two-sided open-channel planar microactuator structure. See, Pollack, et al., Lab Chip Vol. 2, pp 96-101 (2002). Another reported technique system involves water or dodecene microdroplets that float freely on a surface of fluorinated oil and electric fields are applied through an array of electrodes below the surface of the oil phase to manipulate the droplets. Velev et al, Nature Vol. 426, pp 515-516 (2003); Official Digest. Nat. Mater. Vol. 4, pp. 98-102 (2005). Asymmetric laser heating of a liquid/liquid interface between an aqueous droplet and its surrounding immiscible fluid can induce thermal Marangoni flows to move the droplet, which has been demonstrated with a protein assay. Kotz et al, Appl. Phys. Lett. Vol 85, pp. 2658-60 (2004)
A key requirement for many biological and chemical reactions is efficient heating of the sample. For example, the ability to perform the polymerase chain reaction (PCR) with high efficiency in microfluidic environments is critically dependent on rapid and precise heat transfer.
Many heating techniques have been developed for use in microfluidic networks and to droplets on solid surfaces. Non-zonal heating is generally accomplished using a Peltier device, a thin film heater or a laboratory hotplate. Accurate zonal heating may be achieved through the use of complex on-chip resistive heater networks, requiring additional fabrication steps. The primary restrictions associated with these heating methods are the thermal properties and mass of the heating block and the reaction chamber, which ultimately limit the rate at which the sample can be heated and cooled. The thermal mass problem can be eliminated by using non-contact heating methods to specifically heat the sample or the reaction medium. Advanced droplet-based microfluidics is especially problematic due to the required efficient localized heating of the individual droplets with minimal heat transfer to the surroundings.
Porous particles constructed from electrochemically etched porous materials, such as silicon, have widespread application in optoelectronics, chemical and biological sensors, high-throughput screening, and drug delivery applications. These porous particles are especially advantageous because of the relative ease with which the optical properties, pore size, and surface chemistry can be manipulated. Moreover, position, width, and intensity of spectral reflectivity peaks may be controlled by the current density waveform and solution composition used in the electrochemical etch, thus rendering possible the preparation of films of porous particles that display any color within the visible light band with high color saturation, which is a desirable feature for information displays.
Porous particles and films constructed from electrochemically etched porous materials have provided powerful methods for labeling and encoding. Porous particles and films and methods using porous particles and films are disclosed in 1) U.S. Published Patent Application 20050042764, entitled “Optically encoded particles” to Sailor et al., published Feb. 24, 2005; 2) U.S. Published Patent Application 20050009374, entitled “Direct patterning of silicon by photoelectrochemical etching”, to Gao, et al., published Jan. 13, 2005; 3) U.S. Published Patent Application 20030146109 entitled “Porous thin film time-varying reflectivity analysis of samples,” to Sailor, et al. published Aug. 7, 2003; 4) PCT Application PCT/US04/043001, entitled “Optically encoded particles, system and high throughput screening, to Sailor et al, filed Dec. 21, 2004; 5) PCT Application PCT/US04/042997, entitled “Optically encoded particles with grey scale spectra,” to Sailor et al, filed Dec. 21, 2004; and 6) U.S. Published Application 2006025508, entitled, “Photonic Sensor Particles and Fabrication Methods”, to Sailor, et al filed Aug. 13, 2004.